In single machines and in lines with continuous processes for dyeing and ennobling yarns and fabrics there are always tanks that carry out various hot washing operations. In all of these operations there is substantial consumption of water and of heat energy. Environmental and economic requirements to reduce water and heat energy consumption and the need to be able to carry out more efficient washes, required by new wet finishing processes of fabrics, as well as by the standards of the various consumer protection eco-labels, must lead to a solution to this problem being identified.
The efficiency of a wash, both as intermediate operation, and as final operation of a given textile cycle, must not be undervalued. Very often, indeed, the efficiency of the wash is determinant both for the successful outcome of the subsequent operations for the purposes of the quality of the product, and since the washing operation constitutes a substantial part of the processing costs.
A typical ennoblement application of yarns is that of their continuous mercerization and dyeing to produce fabrics commonly called “denim”. Denim is a fabric used to make blue jeans and “sportswear” items in general, and it is the most used fabric in the world. Classic denim is manufactured by weaving pre-dyed cotton threads. In particular, only the warp is dyed continuously, with indigo or other dyes, whereas the weft is used untreated.
In continuous lines for dyeing chains of warp for denim fabric with indigo, the hot washes after the preparatory operations of scouring, pre-dyeing or mercerization are numerous and have the function of eliminating the greatest possible amount of impurities of the threads, consisting of their reaction products and the substances used in the formulation of the treatment bath. In the case of mercerization, for example, it concerns eliminating the sodium hydroxide absorbed by the yarn, so as to avoid use of the neutralisation operation or, at the very least, to reduce the amount of acid necessary for the purpose. The washes after dyeing, on the other hand, have the purpose of eliminating the parts of dye not properly fixed to the fibre, an operation of essential importance for the dyeing quality of the yarn and the subsequent finishing processes of the fabric.
For these operations, one or more tanks are normally used, arranged in line, each of which contains one or more return and guiding cylinders immersed in the washing bath, as well as a pair of wringing cylinders or “foulards” arranged at the outlet of the textile material from the tank. Sometimes, to save water, the tanks are connected through pipes to operate in countercurrent to each other. Although it is a very particular ennoblement process, to wash the thousands of paired threads, such as the chains of warp or warp thread, the normal washing tanks for fabric have still always been used, but with poor washing effect and high specific consumption of water and heat energy.
A certain improvement is obtained with the washing devices illustrated in Italian patents no. 01276825 and no. 01298448 to the same Applicant. The advantages of such washing devices, however, have been practically offset by a series of problems, including that caused by spraying systems that, being able to become blocked locally, cause the breaking down of the organised configuration of the threads, creating harmful creasing and breaking.
Further washing devices for textile materials are described, for example, in documents GB 922 302 A and U.S. Pat. No. 897,133 A. In particular, document GB 922 302 A illustrates a device for intensifying the washing effect able to be used exclusively for washing fabrics. Such a device for intensifying the washing effect, during the rotation and thanks to its polygonal shape, subjects the fabric, intermittently, to flexing, tension and beating action. In the case of use with a warp thread, this would involve the decomposition of the organised configuration of the warp thread with overlapping of threads, with consequent uneven wringing, dyeing and starching and with high probability of the threads breaking. The device for intensifying the washing effect illustrated in document GB 922 302 A is thus unsuitable for washing yarns.
In the device for intensifying the washing effect illustrated in document GB 922 302 A the efficiency of washing is down to the pressure inside a perforated central tube. The pressure is generated by two propellers arranged at the ends of such a tube, respectively. The propellers, in an opposite manner, thrust the washing water inside the perforated central tube. Considering that the cylinders of the normal washing tanks have a maximum outer diameter of 150/160 mm, it can be presumed that the perforated central tube has a maximum diameter of 120/130 mm. In the case of washes for continuously dyed yarns the operative speed is 25/30 metres per minute and therefore the propellers, with diameter 120/130 mm, would rotate at most at 65/70 revs/min., with a negligible flow rate and certainly not capable of creating an internal pressure in a perforated tube. In the case of low-speed processing, the flow rate of the propellers would be practically zero, for which reason the washing efficiency of the device for intensifying the washing effect illustrated in document GB 922 302 A is limited and not constant.
The device for intensifying the washing effect illustrated in document GB 922 302 A is very complex in construction, being provided with a rotation shaft integral with the perforated central tube through inner spokes, a central diaphragm, outer blades with dividing rings, cells, spaces, lateral propellers, etc. In continuous dyeing lines with indigo, concerning eliminating of the pigment not fixed to the fibre from the yarn, this construction, wherein many recesses are provided, lends itself to the formation of deposits of pigment, of fur and of other residues. This can also create clogging or obstruction of the holes of the central tube. The complexity of the device for intensifying the washing effect illustrated in document GB 922 302 A makes the cleaning operation thereof difficult.
The device for intensifying the washing effect illustrated in document U.S. Pat. No. 897,133 A, even with minimal constructive differences, has the same drawbacks as the device for intensifying the washing effect illustrated in document GB 922 302 A in terms of inefficiency and lack of consistency of the washing effect. In particular, there is a functional contradiction that consists of the fact that the device for intensifying the washing effect illustrated in document U.S. Pat. No. 897,133 A would operate on the basis of two mutually conflicting fluid-dynamic principles. Indeed, document U.S. Pat. No. 897,133 A specifies both that in the cylinder, through the respective propellers, a stream of liquid is generated from inside towards outside, and that the liquid will flow readily inside the cylinder through the slits formed on the surface of such a cylinder.